docs: def _title(fig, title, subtitle="", *, margin=1, fontsize=20, subfontsize=18):
      """Add a title to a figure.
  
      Parameters
      ----------
      fig : matplotlib Figure
          Figure.
      title : string
          Title.
      subtitle : string
          Subtitle.
      margin : number (optional)
          Distance from top of plot, in inches. Default is 1.
      fontsize : number (optional)
          Title fontsize. Default is 20.
      subfontsize : number (optional)
          Subtitle fontsize. Default is 18.
      """
      fig.suptitle(title, fontsize=fontsize)
      height = fig.get_figheight()  # inches
      distance = margin / 2.  # distance from top of plot, in inches
      ratio = 1 - distance / height
      fig.text(0.5, ratio, subtitle, fontsize=subfontsize, ha="center", va="top")